High dynamic response valves are known in the art. These valves are often used, in both open and closed servoloops, to control fluid flows and/or fluid pressures in hydraulic systems. These systems may have a bushing movable relative to a body, and a valve spool movable relative to the bushing. The bushing and spool have control edges that are movable relative to one another to vary the sizes of one or more control openings by means of which the fluid parameter is controlled. Heretofore, one of the spool and bushing has been movable relative to the other by means of a direct or indirect drive.
Directly-controlled valves have used electromechanical transformers, proportional magnets, linear motors, plunger coils or piezoelectric converters to move the associated valve member (i.e., either spool or bushing) relative to the body. Directly-controlled valves have the disadvantage that fast reactions can only be realized with short-stroke drivers. Indirectly-controlled valves have used mechanical-hydraulic transformers, pressure-control of spool position, nozzle baffles and nozzle pipes. Highly-dynamic valves have used both direct and servo-assisted control.
In the prior art, either the position of the spool or the bushing relative to the body was varied. Thus, the prior art devices had an active (i.e., movable) control edge and an inactive (i.e., non-movable) control edge. If the spool was movable relative to the bushing, the active edge was on the spool, and the inactive edge was on the bushing. Conversely, if the bushing was movable relative to the spool, then the active edge was on the bushing and the inactive edge was on the spool. The attainable frequency of the valve was determined by the frequency response of the associated valve driver.
Accordingly, it would be generally desirable to provide an improved valve of this spool-bushing type that is capable of improved dynamic response.